The old implementation of vrend_add_formats used to check color readback
format even if a depth buffer is bound. As no texture is attached to the
color buffer for such a FBO, it makes glGetIntegerv with
GL_IMPLEMENTATION_COLOR_READ_TYPE fail, and the error can trigger the
GL_NO_ERROR assertion in the function.
Check only if the depth buffer can be read in such a case.
Signed-off-by: Akihiko Odaki akihiko.odaki@gmail.com